layout/generic/ScrollGeneration.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef mozilla_ScrollGeneration_h_
   6 #define mozilla_ScrollGeneration_h_
   7
   8 #include <cstdint>
   9 #include <iosfwd>
  10
  11 namespace mozilla {
  12
  13 struct ScrollGenerationCounter;
  14
  15 class APZTag {};
  16 class MainThreadTag {};
  17
  18 template <typename Tag>
  19 struct ScrollGeneration;
  20
  21 template <typename Tag>
  22 std::ostream& operator<<(std::ostream& aStream,
  23                          const ScrollGeneration<Tag>& aGen);
  24
  25 template <typename Tag>
  26 struct ScrollGeneration {
  27   friend struct ScrollGenerationCounter;
  28
  29  private:
  30   // Private constructor; use ScrollGenerationCounter to get a new instance.
  31   explicit ScrollGeneration(uint64_t aValue);
  32
  33  public:
  34   // Dummy constructor, needed for IPDL purposes. Not intended for manual use.
  35   ScrollGeneration();
  36
  37   uint64_t Raw() const { return mValue; }
  38
  39   bool operator<(const ScrollGeneration<Tag>& aOther) const;
  40   bool operator==(const ScrollGeneration<Tag>& aOther) const;
  41   bool operator!=(const ScrollGeneration<Tag>& aOther) const;
  42
  43   friend std::ostream& operator<<<>(std::ostream& aStream,
  44                                     const ScrollGeneration<Tag>& aGen);
  45
  46  private:
  47   uint64_t mValue;
  48 };
  49
  50 using APZScrollGeneration = ScrollGeneration<APZTag>;
  51 using MainThreadScrollGeneration = ScrollGeneration<MainThreadTag>;
  52
  53 struct ScrollGenerationCounter {
  54   MainThreadScrollGeneration NewMainThreadGeneration() {
  55     uint64_t value = ++mCounter;
  56     return MainThreadScrollGeneration(value);
  57   }
  58
  59   APZScrollGeneration NewAPZGeneration() {
  60     uint64_t value = ++mCounter;
  61     return APZScrollGeneration(value);
  62   }
  63
  64  private:
  65   uint64_t mCounter = 0;
  66 };
  67
  68 }  // namespace mozilla
  69
  70 #endif  // mozilla_ScrollGeneration_h_